bool isPalindrome(char* s) {
    int j = 0;
    int l = strlen(s);
   for(int i = 0;i<l;i++){
       if(s[i]>='a'&&s[i]<='z'){
           s[j] = s[i];
           j++;
       }else if(s[i]>='A'&&s[i]<='Z'){
           s[j] = s[i]+'a'-'A';
           j++;
       }else if(s[i]>='0'&&s[i]<='9'){
           s[j] = s[i];
           j++;
       }
   } 
   s[j] = '\0';
   for(int k = 0;k<j/2;k++){
       if(s[k]!=s[j-1-k]){
           return false;
       }
   }
   return true;
}